1. Field of the Invention
The invention relates to electro-optical data handling systems that convert light modulation into electrical signals.
2. Description of the Prior Art
Electro-optical data handling systems are known in the art that may be utilized, for example, to transmit data from a computer to a printer. In such apparatus, data signals modulate light that is received by a phototransistor. The phototransistor, in turn, provides an output electrical signal in accordance with the light modulation.
Some of these prior art circuits couple light from a data source through fiber optics to a phototransistor having a resistive load. Although such circuits generally operate satisfactorily, they are, however, sensitive to noise pick up by the electronic circuit components and conductors. Since a primary purpose of a fiber optical system is noise immunity, such prior art noise sensitive transducers tend to obviate this purpose. Additionally, such resistively loaded transducers tend to be limited in speed of response and thus limit the bandwidth of the circuit.
An example of a prior art electro-optical system utilizing light modulation is described in U.S. Pat. No. 4,654,892 issued Mar. 31, 1987. Although the system of said U.S. Pat. No. 4,654,892 operates generally satisfactorily, the device tends to be sensitive to electrical noise pickup as described above. Additionally, the device provides an analog output that is not compatible with present day digital circuitry such as microprocessors which require, for example, TTL signals. A level comparator and wave shaping circuitry are required at the output of the device of said U.S. Pat. No. 4,654,892 to provide an output compatible with digital circuits.